14,473 research outputs found
Excess antisense RNA from infectious recombinant SV40 fails to inhibit expression of a transfected, interferon-inducible gene
Anomalous isotopic predissociation in the F³Πu(v=1) state of O₂
Using a tunable, narrow-bandwidth vacuum-ultraviolet source based on third-harmonic generation from excimer-pumped dye-laser radiation, the F³Πu←X³Σg-(1,0)photoabsorption cross sections of ¹⁶O₂ and ¹⁸O₂ have been recorded in high resolution. Rotational analyses have been performed and the resultant F(v=1) term values fitted to the ³Π Hamiltonian of Brown and Merer [J. Mol. Spectrosc. 74, 488 (1979)]. A large rotationless isotope effect is observed in the F(v=1)predissociation, wherein the Lorentzian linewidth component for ¹⁸O₂ is a factor of ∼50 smaller than the corresponding ¹⁶O₂linewidth. This effect, a consequence of the nonadiabatic rotationless predissociation mechanism, is described using a coupled-channel treatment of the strongly Rydberg-valence-mixed 3Πu states. Significant J, e/f-parity, and sublevel dependencies observed in the isotopic F(v=1) rotational widths are found to derive from an indirect predissociation mechanism involving an accidental degeneracy with the E³Σ−u(v=3) level, itself strongly predissociated by ³Σ−u Rydberg-valence interactions, together with L-uncoupling (rotational) interactions between the Rydberg components of the F and E states. Transitions into the E(v=3) level are observed directly for the first time, specifically in the ¹⁸O₂ spectrumPartial support
was provided by an NSF International Opportunities for Scientists
and Engineers Program Grant No. INT-9513350, and
Visiting Fellowships for G.S. and J.B.W. at the Australian
National University
Pupillometry, a bioengineering overview
The pupillary control system is examined using a microprocessor based integrative pupillometer. The real time software functions of the microprocessor include: data collection, stimulus generation and area to diameter conversion. Results of an analysis of linear and nonlinear phenomena are presented
A spectroscopic search for AGN activity in the reionization era
The ubiquity of Lyman alpha (Ly) emission in a sample of four bright
[O III]-strong star-forming galaxies with redshifts above 7 has led to the
suggestion that such luminous sources represent a distinct population compared
to their fainter, more numerous, counterparts. The presence of Ly
emission within the reionization era could indicate that these sources created
early ionized bubbles due to their unusually strong radiation, possibly due to
the presence of active galactic nuclei. To test this hypothesis we have secured
long integration spectra with XSHOOTER on the VLT for three 7 sources
selected to have similar luminosities and prominent excess fluxes in the IRAC
3.6 or 4.5m band, usually attributed to strong [O III] emission. We
secured additional spectroscopy for one of these galaxies at =7.15 using
MOSFIRE at the Keck telescope. For this, the most well-studied source in our
sample with the strongest IRAC excess, we detect prominent nebular emission
from He II and NV indicative of a non-thermal source. For the other two sources
at =6.81 and =6.85, for which no previous optical/near infrared
spectroscopy was initially available, Ly is seen in one and CIII]
emission in the other. Although a modest sample, our results further support
the hypothesis that the phenomenon of intense [O III] emission is associated
preferentially with sources lying in early ionized bubbles. However, even
though one of our sources at =7.15 clearly indicates the presence of
non-thermal radiation, such ionized bubbles may not uniquely arise in this
manner. We discuss the unique advantages of extending such challenging
diagnostic studies with JWST.Comment: 11 pages, 7 figures, submitted to Ap
A Meinardus theorem with multiple singularities
Meinardus proved a general theorem about the asymptotics of the number of
weighted partitions, when the Dirichlet generating function for weights has a
single pole on the positive real axis. Continuing \cite{GSE}, we derive
asymptotics for the numbers of three basic types of decomposable combinatorial
structures (or, equivalently, ideal gas models in statistical mechanics) of
size , when their Dirichlet generating functions have multiple simple poles
on the positive real axis. Examples to which our theorem applies include ones
related to vector partitions and quantum field theory. Our asymptotic formula
for the number of weighted partitions disproves the belief accepted in the
physics literature that the main term in the asymptotics is determined by the
rightmost pole.Comment: 26 pages. This version incorporates the following two changes implied
by referee's remarks: (i) We made changes in the proof of Proposition 1; (ii)
We provided an explanation to the argument for the local limit theorem. The
paper is tentatively accepted by "Communications in Mathematical Physics"
journa
Soliton blue-shift in tapered photonic crystal fiber
We show that solitons undergo a strong blue shift in fibers with a dispersion
landscape that varies along the direction of propagation. The experiments are
based on a small-core photonic crystal fiber, tapered to have a core diameter
that varies continuously along its length, resulting in a zero-dispersion
wavelength that moves from 731 nm to 640 nm over the transition. The central
wavelength of a soliton translates over 400 nm towards shorter wavelength. This
accompanied by strong emission of radiation into the UV and IR spectral region.
The experimental results are confirmed by numerical simulation.Comment: 10 pages, 4 figure
Engaging postgraduate students and supporting higher education to enhance the 21st century student experience:Final Report
Multiple hydrodynamical shocks induced by Raman effect in photonic crystal fibres
We theoretically predict the occurrence of multiple hydrodynamical-like shock
phenomena in the propagation of ultrashort intense pulses in a suitably
engineered photonic crystal fiber. The shocks are due to the Raman effect,
which acts as a nonlocal term favoring their generation in the focusing regime.
It is shown that the problem is mapped to shock formation in the presence of a
slope and a gravity-like potential. The signature of multiple shocks in XFROG
signals is unveiled
Physical State of Molecular Gas in High Galactic Latitude Translucent Clouds
The rotational transitions of carbon monoxide (CO) are the primary means of
investigating the density and velocity structure of the molecular interstellar
medium. Here we study the lowest four rotational transitions of CO towards
high-latitude translucent molecular clouds (HLCs). We report new observations
of the J = (4-3), (2-1), and (1-0) transitions of CO towards eight
high-latitude clouds. The new observations are combined with data from the
literature to show that the emission from all observed CO transitions is
linearly correlated. This implies that the excitation conditions which lead to
emission in these transitions are uniform throughout the clouds. Observed
13CO/12CO (1-0) integrated intensity ratios are generally much greater than the
expected abundance ratio of the two species, indicating that the regions which
emit 12CO (1-0) radiation are optically thick. We develop a statistical method
to compare the observed line ratios with models of CO excitation and radiative
transfer. This enables us to determine the most likely portion of the physical
parameter space which is compatible with the observations. The model enables us
to rule out CO gas temperatures greater than 30K since the most likely
high-temperature configurations are 1 pc-sized structures aligned along the
line of sight. The most probable solution is a high density and low temperature
(HDLT) solution. The CO cell size is approximately 0.01 pc (2000 AU). These
cells are thus tiny fragments within the 100 times larger CO-emitting extent of
a typical high-latitude cloud. We discuss the physical implications of HDLT
cells, and we suggest ways to test for their existence.Comment: 19 pages, 13 figures, 2 tables, emulateapj To be published in The
Astrophysical Journa
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